Clutches (also called drives or couplings) are used in a variety of contexts to selectively control torque transmission between an input and an output. For instance, fan clutches are used to control rotation of a fan, such as a cooling fan for an automotive or industrial application. Controlled operation of a cooling fan provides all the benefits associated with cooling flows when the clutch is engaged, but also allows the fan to be turned off when not needed, thereby reducing parasitic losses and increasing fuel efficiency. Turning off a cooling fan can also allow additional power to be diverted to other uses.
In certain light duty applications, such as for small industrial equipment like miniature excavators, generators, light towers, and material handling equipment, there are severe space constraints available that limit the use of a fan clutch. Many of these applications do not include any fan clutch and currently use a fan that is directly driven by a pulley on the engine. These types of “always on” cooling fan arrangements are compact, but are far from optimal in terms of fuel burn and parasitic losses. The space to introduce a fan drive was never taken into account in the design. Furthermore, many of these applications utilize a fan that is mounted on the water pump, primarily so that the same belt drive system can be used to power both the water flow and the fan, saving cost and complexity. However, many of the water pumps were designed to support the mass of the fan only. Increased weight introduced by a fan clutch may require larger bearings in the water pump, increasing size and cost of the water pump. Moreover, because the fan (and fan clutch) is hung in front of the water pump bearing system, the length is an equally large factor in the amount of overhung load need to be carried by the bearing system.
While some relatively small bimetal-controlled viscous fan clutches are available, many industrial applications utilize blower fans rather than sucker fans, meaning that relatively hot air is blown out from an engine compartment rather than relatively cool air being sucked into the engine compartment. Bimetal controlled viscous clutches are not suitable for such blower applications, because the heat from the engine compartment air would tend to keep the clutch engaged all or almost all of the time.
Therefore, it is desired to provide a controllable fan drive that has a compact size suitable for light duty applications. Furthermore, or in the alternative, it is desired to provide an electromagnetic coil assembly suitable for suit in a compact viscous clutch.